I'm migrating my smoke alarms from the main panel to a generator-backed-up subpanel so I'll have fire protection during a power outage. I'm simultaneously replacing the old smoke detectors.

I read that smoke detectors should be on an AFCI protected circuit, but the instruction manuals for both my Kidde Firex Smoke Alarm and my Kidde Firex Heat Alarm say:

The appropriate power source is 120 Volt AC Single Phase supplied from a non-switchable circuit which is not protected by a ground fault interrupter.

My Siemens Combination Type Arc-Fault Circuit Interrupter breaker says

Detects line-to-neutral, line-to-ground and series arcs!

Does that mean it's a "ground-fault interrupter" so I shouldn't use it with the alarms?

  • 1
    You don't want circuit protection on protective circuits. For instance if a sprinkler system has an emergency diesel engine to pressurize the system (e.g. in a power outage) -- it will NOT have shut-offs for low oil pressure, coolant, temp, etc. The purpose is to protect the building, not the engine. Commented Dec 19, 2016 at 21:28

1 Answer 1


You can have them on an AFCI circuit if you like. Newer codes would require it, but if they are not on an AFCI now you do not need to add one just because you are moving the circuit the generator panel.

No, newer "combination AFCI" breaker are NOT combination AFCI/GFCI breakers. It means they detect parallel and series arc faults.

  • I guess I still don't understand the difference between ground faults and line-to-ground arc faults. Thanks for steering me right, though.
    – Michael H
    Commented Dec 1, 2014 at 12:50
  • @MichaelH, a ground fault is anything that causes the power coming in on the hot wire to be greater than the power going out on the neutral wire -- the assumption is that the missing power is going to ground somewhere. A line-to-ground arc fault is a particular type of ground fault, when the hot conductor comes into near contact with something grounded, generating a spark that rapidly heats things up, possibly causing a fire. (Solid contact between hot and ground would be a short circuit, which would trip the circuit breaker.)
    – Mark
    Commented Jan 10, 2020 at 3:42
  • I thought the code only pertained to 120V, 15/20A circuits with a receptacle on it. How does that apply to smoke detectors?
    – mreff555
    Commented Jul 14, 2020 at 22:59
  • @mreff555, it applies to circuit with outlets. All receptacles are outlets, but not all outlets are receptacles. Commented Nov 28, 2020 at 19:43
  • Ok, so how is an outlet defined? Are you implying that because of the pigtail, it qualifies as an outlet which needs an AFCI?
    – mreff555
    Commented Nov 28, 2020 at 20:51

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